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Johnp292 · 07-11-2015, 06:34 PM

So I tried my mini tune up today, after 2 frustrating weeks of waiting for parts from Cummins. They still haven't arrived, even after they promised to overnight them to me on Thursday, so I gave up and went to an RV dealer for the part$. They had everything I needed except the oil filter, so the oil change will have to wait. I replaced the plugs, the air filter and the fuel filter. I think the ones I took out were the originals from 1997. After each step I tried to start the generator. No joy. The fuel filter was the last, and most difficult thing I changed. When I finally got the fuel line off the old filter, there was no residual fuel in either the line or the filter. I tried cranking the generator with the hose off and got nothing. So now I'm back to suspecting the pump is bad (yes my fuel tank is full). I'm unsure if replacing the pump is something I want to try myself. It seems pretty inaccessible to me but I could try to overcome that. My biggest concern is how do I prevent a major gasoline spill when I disconnect the fuel line from the tank to the old pump? Any advice? We're getting a little frustrated as we can't use the RV in the Arizona summer without the house AC units.

bhale · 07-12-2015, 05:26 AM

Fuel should not run out as the line should be higher than the tank.

Johnp292 · 07-18-2015, 01:04 PM

Is there a fuel filter inline before the pump? Instructions for the new pump say there should be.

Johnp292 · 07-19-2015, 04:12 PM

So I got a friend to help me try to replace the fuel pump today. Using an inspection mirror and an extra pair of hands, getting the pump out wasn't that bad. I went under the RV and disconnected the power leads (after d/c-ing the battery) and my helper reached over the engine and removed the (only 2!) nuts holding the pump to the bracket. Watching from below I was able to help guide him to the top of the pump. But then as I started working the pump down through the opening, I saw that the hose from the "out" side of the pump to the generator was severely crimped due to the angle at which it had been installed. The hose was connected to a safety valve that was directly connected to the fuel pump. The severity of the crimp certainly could have restricted the fuel flow. However, it had also caused damage to the hose to the extent there is now a hole in it. We removed the hose and set out to try a few auto parts stores and the RV dealer looking for a replacement. No luck, but the RV dealer referred me to a custom hose shop that happens to be right near where I work, so I'm going there tomorrow to see about having a replacement made. Another weekend lost.

What's confusing me is that I'm quite certain that prior to the issue I'm having now, there were no fuel leaks when using the generator, nor did any fuel leak out when I tested the fuel flow last weekend. Is it somehow possible that the hole is a new development that has caused that safety valve to cut off the fuel flow?

We did not complete the removal of the old pump, so my plan is to try another flow test once I get a new hose to see if I still need to replace the pump, or if the crimped hose was the culprit all along.

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bhale · 07-20-2015, 05:05 AM

Mine does not have a filter.

bhale · 07-20-2015, 05:09 AM

The line looks like it was twisted either in instalation or removing it. I have saw people damage the lines by not using a wrench to keep line from twisting.

mojoracing · 07-20-2015, 05:34 AM

I have said this at least 20 times. If the usual low oil or gunked up carb are not the problem, the first place u go is fuel pump on an onan. They go bad all the time.

ga traveler · 07-20-2015, 01:18 PM

Quote:

Originally Posted by mojoracing

I have said this at least 20 times. If the usual low oil or gunked up carb are not the problem, the first place u go is fuel pump on an onan. They go bad all the time.

I have posted this many times.The pump Onan uses is a vane pump. They are very dependable. Onan calls for a filter before the pump. Trash clogs the vanes in the pump and it stops pumping. make sure you install a filter BEFORE the pump.

Steady_Rest · 07-21-2015, 09:38 AM

Recently my Onan generator would crank but not start for the first time in 22 years. All the components were original except the spark plugs. There is a lot of information on how to diagnose these units on line. The first item I checked was voltage to the fuel pump which was zero, so I suspected the control board might be bad. Back probing the board connectors for voltage while cranking showed why the fuel pump had no power. Further testing of the board revealed a bad relay as the cause of my trouble, which I suspected. Relays are quite often the problem on control boards. Because I was preparing to go on a trip and now late, a board was ordered from Flight Systems with overnight delivery, but this was still cheaper than Cummins. Save your old board, the relays are available to repair the board for a few dollars. This was what I did and now have a second functioning board for backup.
After installing the new board the gen. started right up, but my troubles continued. I ran the gen. for about 15 min. and all seemed well. The next day after starting, the unit shut itself down and would not restart. Remembering that a few times in the past the remote switch inside the rv had failed, I unplugged the remote switch connector from the control board and the gen. again ran with no problem. There was a short in the remote switch which caused the shut down.
I post this in case it might help someone in the future with a crank but no start condition. It can be time consuming to pin point a problem but I prefer to know what has failed and not replace parts with crossed fingers. That method I find too gut wrenching, with my machine mocking me with failure. Problems can come in pairs making diagnoses even more frustrating.

Kevin

Johnp292 · 08-01-2015, 10:29 AM

Well the fuel pump is replaced, new hose is in place, the generator starts fine and purrs like a kitten when idling, but as soon as I put a load on it, it stalls within 3-5 minutes. It will immediately start up again just fine, but same thing, idle it seems to run great, under load it stalls. I tried spraying carb cleaner in and running SeaFoam through the gas tank, and I actually managed to get it to run with the smaller bedroom AC for about 15 minutes - until the CO detector went off and cut off the fuel. But that was a one time deal, I haven't been able to get it to run under load again. With the big front AC on it stalls almost immediately. It will start producing a little black smoke just before it stalls. The AC units work fine on shore power. At this point I suspect it needs a new carburetor (you can't clean them on this model, only replace them!), unless anyone has a better idea?

ga traveler · 08-02-2015, 08:09 AM

Are you using the Onan 4C carb and combustion chamber cleaner? Did you get the generator hot and did you spray the cleaner wide open until you drowned the generator and then let it set for 15 minutes and then restart? The black smoke makes it sound like the trottle is advancing, but to double check, Trip the breakers. Turn on the AC's. Go to the generator and reset the breakers while you watch the throttle lever. If the lever advances and tries to give it more gas, that tells you the speed sensing circuit is working.

Johnp292 · 08-02-2015, 11:42 AM

Quote:

Originally Posted by ga traveler

Are you using the Onan 4C carb and combustion chamber cleaner? Did you get the generator hot and did you spray the cleaner wide open until you drowned the generator and then let it set for 15 minutes and then restart? The black smoke makes it sound like the trottle is advancing, but to double check, Trip the breakers. Turn on the AC's. Go to the generator and reset the breakers while you watch the throttle lever. If the lever advances and tries to give it more gas, that tells you the speed sensing circuit is working.

I thought 4C was no longer available? Other than that, yes I followed the procedure you described.

ga traveler · 08-03-2015, 07:46 AM

Quote:

Originally Posted by Johnp292

I thought 4C was no longer available? Other than that, yes I followed the procedure you described.

That is possible. I retired in 2005. Was called back in two days a week and finally retired in Jan. 1 2009. So, I don't know much about the changes in the last 6 years. Sometimes it comes back to bite me. A while back I was telling someone to make sure they did not use extended life antifreeze in their 1999 F-53. I had talked to the engineer at Ford who designed the V-10. He said only the green antifreeze could be used in the early model V-10. Someone posted a notice from Ford that said it was now O.K. to use the extended life antifreeze in the early V-10. Things do change.

deltadawn90 · 09-26-2015, 11:56 AM

We are having the same problems with our generator Onan marquis 5000. It ran fine last year and wouldn't crank this spring. My husband has worked all summer on it and he can usually fix anything mechanically. We are thinking of ordering a carberator also but they are so expensive if that doesn't fix it.